Method for operating an optical transmission system

Abstract

An optical transmission system method including generating for a tunable laser a pilot tone having an adjustable pilot tone frequency identifying a wavelength division multiplexing channel used by the tunable laser; multiplying the pilot tone with pilot tone data to provide a pilot tone data signal; supplying the pilot tone data signal and a high frequency data signal to the tunable laser generating an optical laser signal output by the tunable laser responsive to the supplied signals; transporting the optical laser signal to a central wavelength to locker; converting the received optical laser signal to provide a pilot tone data signal for wavelength division multiplexing channels demodulated to detect the pilot tone and the pilot tone data for each individual wavelength division multiplexing channel; and identifying the wavelength division multiplexing channel on the basis of the pilot tone frequency of the detected pilot tone and evaluating the pilot tone data.

The invention claimed is: 
     
       1. A method for operating an optical transmission system, the method comprising:
 (a) generating for a tunable laser of a first terminal a pilot tone having an adjustable pilot tone frequency which identifies a wavelength division multiplexing channel used by the respective tunable laser; 
 (b) modulating the generated pilot tone of said tunable laser with pilot tone data to provide a pilot tone data signal; 
 (c) supplying the pilot tone data signal and a high frequency data signal to said tunable laser which generates an optical laser signal output by said tunable laser in response to the supplied signals; 
 (d) transporting said optical laser signal to a remote central wavelength locker of a second terminal via an optical transport medium; 
 (e) converting the received optical laser signal by means of a photo diode of said remote central wavelength locker to provide a pilot tone data signal for wavelength division multiplexing channels which is demodulated to detect the pilot tone and the pilot tone data for each individual wavelength division multiplexing channel; 
 (f) identifying the wavelength division multiplexing channel used by the respective tunable laser on the basis of the pilot tone frequency of the detected pilot tone and evaluating the pilot tone data of the identified wavelength division multiplexing channel; 
 (g) splitting in the remote central wavelength locker the received optical laser signal into a first signal part which is filtered by an etalon filter and applied to an etalon photo diode and into a second signal part which is applied directly to a reference photo diode; 
 (h) comparing the pilot tone amplitude at the reference photo diode and at the etalon photo diode to monitor whether the wavelength of the respective optical laser signal does match a predetermined target wavelength and/or whether the amplitude of the optical laser signal matches a predetermined target power; and 
 (i) controlling the wavelength and/or the power of the tunable laser by said second terminal by transmitting a feedback control signal via a downstream embedded communication channel to said first terminal to adjust the respective tunable laser in response to the received feedback control signal. 
 
     
     
       2. The method according to  claim 1 , wherein at least one wavelength is terminated at said first terminal, and wherein a multitude of wavelengths is terminated at said second terminal. 
     
     
       3. The method according to  claim 1 , wherein the pilot tone data signal and the high frequency data signal are added to generate a laser control signal applied to the tunable laser which generates the optical laser signal output by said tunable laser in response to said laser control signal. 
     
     
       4. The method according to  claim 1 , wherein said high frequency data signal is provided for transporting data at a high data rate of at least 100 Mbit/sec and said pilot tone data signal is provided for transporting control data at a low data rate. 
     
     
       5. The method according to  claim 1 , wherein the demodulation is performed by a Fourier transformation, by a filter or by a filter bank. 
     
     
       6. The method according to  claim 1 , wherein the identifying of the wavelength division multiplexing channel is performed without locking the respective wavelength. 
     
     
       7. The method according to  claim 4 , wherein the control data transported by said pilot tone data signal comprises an identifier of the respective first terminal, a vendor identifier and/or status information data. 
     
     
       8. An optical line terminal comprising:
 a central wavelength locker, comprising:
 at least one photo diode, which is converting a received optical laser signal to provide a pilot tone data signal for wavelength division multiplexing channels, 
 a L/C splitter, which splits the received optical laser signal into a first signal part and a second signal part, 
 an etalon filter which filters the first signal part, 
 an etalon photo diode, which receives the first signal part filtered by the etalon filter, and 
 a reference photo diode, which receives the second signal part; 
 
 a demodulator, which is demodulating the pilot tone data signal to detect a pilot tone and pilot tone data for each individual wavelength division multiplexing channel, 
 
       wherein the detected pilot tone is used to identify the wavelength division multiplexing channel used by a remote tunable laser on the basis of a pilot tone frequency of the detected pilot tone;
 a comparison unit adapted to compare the pilot tone amplitude at the reference photo diode and at the etalon photo diode to monitor whether the wavelength of the respective optical laser signal does match a predetermined target wavelength and/or whether the amplitude of the optical laser signal matches a predetermined target power; and 
 a controlling unit adapted to control the wavelength and/or the power of said remote tunable laser by said second terminal by transmitting a feedback control signal via a downstream embedded communication channel to said remote tunable laser to adjust the respective tunable laser in response to the received feedback control signal. 
 
     
     
       9. An optical transmission system comprising at least one optical network unit, comprising:
 a generator, which is generating a pilot tone having an adjustable pilot tone frequency which identifies a wavelength division multiplexing channel used by the respective tunable laser, 
 a modulation unit, which is modulating the generated pilot tone of said tunable laser with pilot tone data to provide a pilot tone data signal which is supplied along with a high frequency data signal to said tunable laser which generates an optical laser signal output by said tunable laser in response to the supplied signals; 
 an optical line terminal comprising:
 a central wavelength locker, comprising:
 at least one photo diode, which is converting a received optical laser signal to provide a pilot tone data signal for wavelength division multiplexing channels, 
 a L/C splitter, which splits the received optical laser signal into a first signal part and a second signal part, 
 an etalon filter which filters the first signal part, 
 an etalon photo diode, which receives the first signal part filtered by the etalon filter, and 
 a reference photo diode, which receives the second signal part; 
 
 a demodulator adapted to demodulate the pilot tone data signal to detect a pilot tone and pilot tone data for each individual wavelength division multiplexing channel; 
 a comparison unit, comparing the pilot tone amplitude at the reference photo diode and at the etalon photo diode to monitor whether the wavelength of the respective optical laser signal does match a predetermined target wavelength and/or whether the amplitude of the optical laser signal matches a predetermined target power; and 
 a controlling unit, which controls the wavelength and/or the power of said tunable laser by said second terminal by transmitting a feedback control signal to said first terminal to adjust the respective tunable laser in response to the received feedback control signal, 
 
 wherein the detected pilot tone is used to identify the wavelength division multiplexing channel used by a remote tunable laser on the basis of a pilot tone frequency of the detected pilot tone; 
 a downstream embedded communication channel, which is transmitting the feedback control signal from said second terminal to said first terminal; and 
 an optical transport medium, which is transporting the optical laser signal from said optical network unit to said optical line terminal. 
 
     
     
       10. The optical transmission system according to  claim 9 , wherein several optical network units are connected in parallel to an arrayed wavelength grating, which is multiplexing the optical laser signal output by the optical network units in a first band upstream on said optical transport medium and demultiplexing an optical laser signal received via said optical transport medium in a second band downstream to said optical network units. 
     
     
       11. The optical transmission system according to  claim 9 , wherein said optical line terminal is located at a central office connected to a remote node via said optical transport medium comprising at least one glass fibre, wherein said remote node comprises an arrayed waveguide grating being connected to several optical network units of clients.